The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:
3GPP third generation partnership project
AP access point
BSS basic service set
D2D device to device
eNB evolved NodeB
IBSS independent basic service set
ID identification, identifier
IEEE Institute of Electrical and Electronics Engineers
ISM industrial, scientific, medical
LTE long term evolution (evolved UTRAN)
M2M machine to machine
MAC medium access control
RAT radio access technology
RNTI radio network temporary identifier
SFN system frame number
STA station
UE user equipment
UTRAN universal terrestrial radio access network
WLAN wireless local area network
In the wireless communication arts there has been increasing research into D2D communications in which portable radio devices (two or more) form their own ad hoc network to communicate directly with one another without having to send their data through a conventional (cellular) network. M2M is a subset of D2D in that the M2M communications are typically between un-manned user devices, such as remotely mounted sensors and data collection/aggregation nodes which collect and analyze data from several such sensors for event-based reporting of abnormal conditions. Typically M2M devices will have lesser processing power than their user-operated D2D companions but sometimes need not rely on a temporary power source (unlike a UE radio which relies on a battery for portable power). The following discussion of D2D includes the M2M subset unless specifically noted otherwise.
In some implementations the radio spectrum these D2D devices use for their D2D communications lies in the unlicensed frequency bands, such as the ISM band in which WLAN communications occur or what is known as television whitespaces. In others it lies in a cellular band, either from opportunistic use of spectrum ‘holes’ the mobile devices find and exploit while avoiding interference to the primary (conventional cellular) users on that licensed band, or by being allocated certain radio resources by the cellular network itself for their D2D communications. In any of these the cellular network might exercise some varying level of control over the D2D communications in order to assure a more efficient use of the limited radio spectrum.
FIG. 1 illustrates an exemplary wireless environment in which embodiments of these teachings may be practiced to advantage. Cell A is a cellular region in which UEs operating on the licensed band are controlled by an eNB 22, and is adjacent to cell B which is controlled by eNB 23. Near the border there is a cluster of UEs (UE1, UE2, UE3, UE4) which seek to engage in D2D communications.
In conventional infrastructure mode WLAN each UE not operating as the AP for the group would be associated to a given AP by responding to the AP's beacon requesting to associate to the AP's group, termed a BSS. The AP coordinates communications, some of which may be D2D, and also provides the UEs (termed non-AP STAs in WLAN) with connectivity to a broader network such as the Internet. In conventional ad hoc mode WLAN there is no AP and so no AP's beacon to which the STAs can associate. In this case one of the STAs takes on some limited functions of the AP by transmitting its own beacon using an IBSS ID it selects; the other STAs join that IBSS and the joined devices can then engage in D2D communications. Unlike the infrastructure mode, the D2D devices in the ad hoc mode must discover one another without the aid of a centralized AP to which all interested devices in the area are associated.
D2D is not nearly as ubiquitous as other communication techniques, but it is anticipated that some proximity-based or location-based applications might be added to broaden its usability. See for example document Tdoc RP-110706 entitled ON THE NEED FOR A 3GPP STUDY ON LTE DEVICE-TO-DEVICE DISCOVERY AND COMMUNICATION; Tdoc RP-110707 entitled STUDY ON LTE DEVICE TO DEVICE DISCOVERY AND COMMUNICATION—RADIO ASPECTS; and Tdoc-RP-110708 entitled STUDY ON LTE DEVICE TO DEVICE DISCOVERY AND COMMUNICATION—SERVICE AND SYSTEM ASPECTS (each from 3GPP TSG-RAN #52; Bratislava, Slovakia; 31 May to 3 Jun. 2011; by Qualcomm Inc.).
In the inventors' view D2D in its current state is not seen to be well adapted for very wide adoption; the current protocols for device discovery in the radio/physical layer may tend to flood the higher layers (MAC and L1 layers) if the lower radio/physical layers have to pass all the D2D discovery signaling they detect to the upper layers for processing and decision making. If D2D were more common the devices seeking to join an ad hoc IBSS would be scanning and reading many beacons which they then disregard after decoding and deciding that they choose not to join. The IEEE 802.11mb specifications which give the beacon frame format note that the beacon frame is a subtype of a management frame, and that the beacon frame origins are separated by the BSS/IBSS ID field and the sender's MAC address field, both in the header. Additionally, the current D2D protocols do not seem to support proximity-based or location-based applications as the above 3GPP documents seek.